diff --git a/i/n/j.h b/i/n/j.h
index e11c76ffe..0ca8b55ef 100644
--- a/i/n/j.h
+++ b/i/n/j.h
@@ -68,7 +68,6 @@
       extern u3j_dash u3j_Dash;
 #     define u3D u3j_Dash
 
-
     /**  Functions.
     **/
       /* u3j_boot(): initialize jet system.
diff --git a/i/n/t.h b/i/n/t.h
index 99fffee7c..2fa0f0062 100644
--- a/i/n/t.h
+++ b/i/n/t.h
@@ -2,8 +2,51 @@
 **
 ** This file is in the public domain.
 */
+  /**  Options.
+  **/
+    /* U3_CPU_DEBUG: activate profiling.
+    */
+#     define U3_CPU_DEBUG
+
+  /** Data structures.
+  **/
+    /* u3t_trace: fast execution flags.
+    */
+      typedef struct _u3t_trace {
+        c3_o noc_o;                 //  now executing in nock interpreter
+        c3_o glu_o;                 //  now executing in jet glue
+        c3_o mal_o;                 //  now executing in allocator
+        c3_o far_o;                 //  now executing in fragmentor.
+      } u3t_trace;
+
+  /**  Macros.
+  **/
+#   ifdef U3_CPU_DEBUG
+#     define u3t_on(var)  \
+        (u3T.var = (u3C.wag_w & u3o_debug_cpu) \
+                 ? (c3n == u3T.var) ? c3y : (abort(), 0) \
+                 : u3T.var)
+#   else
+#     define u3t_on(var)
+#endif
+
+#   ifdef U3_CPU_DEBUG
+#     define u3t_off(var) \
+        (u3T.var = (u3C.wag_w & u3o_debug_cpu) \
+                 ? (c3y == u3T.var) ? c3n : (abort(), 0) \
+                 : u3T.var)
+#   else
+#     define u3t_off(var)
+#endif
+
+
   /**  Functions.
   **/
+    /* u3t_init(): initialize tracing layer.
+    */
+      void
+      u3t_init(void);
+
     /* u3t_push(): push on trace stack.
     */
       void
@@ -58,3 +101,12 @@
     */
       void
       u3t_boot(void);
+
+
+  /** Globals.
+  **/
+    /* u3_Trace / u3C: global memory control.
+    */
+      c3_global u3t_trace u3t_Trace;
+#     define u3T u3t_Trace
+
diff --git a/n/a.c b/n/a.c
index fee1976bb..2448d21bd 100644
--- a/n/a.c
+++ b/n/a.c
@@ -4,8 +4,6 @@
 */
 #include "all.h"
 
-extern int SAM, SAZ;
-
 /* _box_slot(): select the right free list to search for a block.
 */
 c3_w
@@ -337,11 +335,12 @@ _ca_willoc(c3_w len_w, c3_w ald_w, c3_w alp_w)
 static void*
 _ca_walloc(c3_w len_w, c3_w ald_w, c3_w alp_w)
 {
-  void* ptr_v = _ca_willoc(len_w, ald_w, alp_w);
+  void* ptr_v;
+  
+  u3t_on(mal_o);
+  ptr_v = _ca_willoc(len_w, ald_w, alp_w);
+  u3t_off(mal_o);
 
-  if ( SAM ) {
-    SAZ += len_w;
-  }
 #if 0
   if ( SUB ) {
     fprintf(stderr, "sub: at %p; kid %p\r\n", 
@@ -375,14 +374,14 @@ _ca_walloc(c3_w len_w, c3_w ald_w, c3_w alp_w)
   return ptr_v;
 }
 
-int FOO;
-
 /* u3a_walloc(): allocate storage words on hat.
 */
 void*
 u3a_walloc(c3_w len_w)
 {
-  void* ptr_v = _ca_walloc(len_w, 1, 0);
+  void* ptr_v;
+ 
+  ptr_v = _ca_walloc(len_w, 1, 0);
 
 #if 0
   if ( (703 == u3_Code) &&
@@ -394,9 +393,7 @@ u3a_walloc(c3_w len_w)
       u3a_box* box_u = u3a_botox(ptr_v);
 
       box_u->cod_w = 999;
-      FOO = 1;
     }
-    // if ( 9 == xuc_i ) { FOO = 1; }
     xuc_i++;
   }
 #endif
@@ -436,9 +433,14 @@ u3a_wfree(void* tox_v)
   u3a_box* box_u = u3a_botox(tox_v);
   c3_w*      box_w = (c3_w *)(void *)box_u;
 
+  u3t_on(mal_o);
+
   c3_assert(box_u->use_w != 0);
   box_u->use_w -= 1;
-  if ( 0 != box_u->use_w ) return;
+  if ( 0 != box_u->use_w ) {
+    u3t_off(mal_o);
+    return;
+  }
 
 #if 0
   /* Clear the contents of the block, for debugging.
@@ -512,6 +514,7 @@ u3a_wfree(void* tox_v)
       _box_attach(box_u);
     }
   }
+  u3t_off(mal_o);
 }
 
 #if 0
@@ -1179,16 +1182,17 @@ top:
 u3_noun
 u3a_gain(u3_noun som)
 {
+  // u3t_on(mal_o);
   c3_assert(u3_none != som);
 
-  if ( _(u3a_is_cat(som)) ) {
-    return som;
-  }
-  else {
-    return _(u3a_is_north(u3R))
+  if ( !_(u3a_is_cat(som)) ) {
+    som = _(u3a_is_north(u3R))
               ? _me_gain_north(som)
               : _me_gain_south(som);
   }
+  // u3t_off(mal_o);
+
+  return som;
 }
 
 /* u3a_lose(): lose a reference count.
@@ -1196,6 +1200,7 @@ u3a_gain(u3_noun som)
 void
 u3a_lose(u3_noun som)
 {
+  // u3t_on(mal_o);
   if ( !_(u3a_is_cat(som)) ) {
     if ( _(u3a_is_north(u3R)) ) {
       _me_lose_north(som);
@@ -1203,6 +1208,7 @@ u3a_lose(u3_noun som)
       _me_lose_south(som);
     }
   }
+  // u3t_off(mal_o);
 }
 
 /* u3a_use(): reference count.
diff --git a/n/j.c b/n/j.c
index 3f6b26ce6..f56878ea8 100644
--- a/n/j.c
+++ b/n/j.c
@@ -578,11 +578,13 @@ u3_weak
 u3j_kick(u3_noun cor, u3_noun axe)
 {
   if ( !_(u3du(cor)) ) { return u3_none; } 
+
+  u3t_on(glu_o);
   {
     u3_noun bat = u3h(cor);
     u3_weak cax = u3j_find(bat);
 
-    if ( u3_none == cax ) { return u3_none; }
+    if ( u3_none == cax ) { u3t_off(glu_o); return u3_none; }
     {
       u3_noun mop = u3t(u3h(u3t(cax)));
       u3_noun hap = u3h(u3t(u3h(cax)));
@@ -590,13 +592,14 @@ u3j_kick(u3_noun cor, u3_noun axe)
       u3_noun inx = u3kdb_get(u3k(hap), u3k(axe));
 
       if ( u3_none == inx ) {
-        u3z(cax); return u3_none;
+        u3z(cax); u3t_off(glu_o); return u3_none;
       }
 #if 1
       else if ( !_(_cj_fine(cup, mop, cor)) ) {
         fprintf(stderr, "improper core %x\r\n", u3r_mug(cor));
-        u3m_p("improper core for label", u3h(u3t(u3t(u3h(cax)))));
-        abort();
+        u3m_p("improper label", u3h(u3t(u3t(u3h(cax)))));
+
+        u3t_off(glu_o); 
         return u3_none;
       }
 #endif
@@ -612,8 +615,9 @@ u3j_kick(u3_noun cor, u3_noun axe)
         if ( _(pof_o) ) {
           pof_o = u3t_come(bat);
         }
+        u3t_off(glu_o);
         pro = _cj_kick_z(cor, cop_u, ham_u, axe);
-        
+ 
         if ( u3_none == pro ) {
           if ( _(pof_o) ) {
             pro = u3n_nock_on(cor, u3nq(9, axe, 0, 1));
@@ -765,6 +769,7 @@ u3j_mine(u3_noun clu, u3_noun cor)
   u3_noun bat = u3h(cor);
   u3_noun cax;
 
+  u3t_on(glu_o);
   if ( !_(u3du(cor)) ) {
     u3z(clu);
   }
@@ -780,6 +785,7 @@ u3j_mine(u3_noun clu, u3_noun cor)
     }
   }
   u3z(cor);
+  u3t_off(glu_o);
 }
 
 /* _cj_cold_reap_to: reap clog map.  RETAINS `sab`, TRANSFERS `bas`.
diff --git a/n/m.c b/n/m.c
index bc3069b66..252cbc842 100644
--- a/n/m.c
+++ b/n/m.c
@@ -808,6 +808,10 @@ u3m_soft_top(c3_w    sec_w,                     //  timer seconds
   _cm_signal_deep(0);
 
   if ( 0 != (sig_l = sigsetjmp(u3_Signal, 1)) ) {
+    //  reinitialize trace state
+    //
+    u3t_init();
+
     //  return to blank state
     //
     _cm_signal_done();
@@ -927,6 +931,8 @@ u3m_soft_run(u3_noun fly,
     pro = u3nc(0, u3m_love(pro));
   }
   else {
+    u3t_init();
+
     /* Produce - or fall again.
     */
     {
@@ -1011,6 +1017,8 @@ u3m_soft_esc(u3_noun sam)
     pro = u3m_love(pro);
   }
   else {
+    u3t_init();
+
     /* Push the error back up to the calling context - not the run we
     ** are in, but the caller of the run, matching pure nock semantics.
     */
@@ -1431,6 +1439,10 @@ u3m_boot(c3_o nuu_o, c3_o bug_o, c3_c* dir_c)
   */
   nuu_o = u3e_live(nuu_o, dir_c);
 
+  /* Activate tracing.
+  */
+  u3t_init();
+
   /* Construct or activate the allocator.
   */
   _cm_pave(nuu_o, bug_o);
diff --git a/n/n.c b/n/n.c
index 8bf851054..ba5e3ddc4 100644
--- a/n/n.c
+++ b/n/n.c
@@ -4,15 +4,15 @@
 */
 #include "all.h"
 
-extern int FOO;
+static u3_noun _n_nock_on(u3_noun bus, u3_noun fol);
 
-/* _cn_hint(): process hint.
+/* _n_hint(): process hint.
 */
 static u3_noun
-_cn_hint(u3_noun zep, 
-         u3_noun hod,
-         u3_noun bus,
-         u3_noun nex)
+_n_hint(u3_noun zep, 
+        u3_noun hod,
+        u3_noun bus,
+        u3_noun nex)
 {
   switch ( zep ) {
     default: {
@@ -20,7 +20,7 @@ _cn_hint(u3_noun zep,
       u3a_lose(zep);
       u3a_lose(hod);
 
-      return u3n_nock_on(bus, nex);
+      return _n_nock_on(bus, nex);
     }
 
     case c3__hunk:
@@ -40,19 +40,21 @@ _cn_hint(u3_noun zep,
                u3t(u3t(u3t(hod))));
       }
 #endif
-      pro = u3n_nock_on(bus, nex);
+      pro = _n_nock_on(bus, nex);
       u3t_drop();
 
       return pro;
     }
 
     case c3__slog: {
+      u3t_off(noc_o);
       u3t_slog(hod);
-      return u3n_nock_on(bus, nex);
+      u3t_on(noc_o);
+      return _n_nock_on(bus, nex);
     }
 
     case c3__germ: {
-      u3_noun pro = u3n_nock_on(bus, nex);
+      u3_noun pro = _n_nock_on(bus, nex);
 
       if ( c3y == u3r_sing(pro, hod) ) {
         u3z(pro); return hod;
@@ -62,16 +64,19 @@ _cn_hint(u3_noun zep,
     }
 
     case c3__fast: {
-      u3_noun pro = u3n_nock_on(bus, nex);
+      u3_noun pro = _n_nock_on(bus, nex);
 
+      u3t_off(noc_o);
       u3j_mine(hod, u3k(pro));
+      u3t_on(noc_o);
+
       return pro;
     }
 
     case c3__memo: {
       u3z(hod);
 #if 0
-      return u3n_nock_on(bus, nex);
+      return _n_nock_on(bus, nex);
 #else
       {
         u3_noun pro = u3z_find_2(c3__nock, bus, nex);
@@ -80,7 +85,7 @@ _cn_hint(u3_noun zep,
           u3z(bus); u3z(nex);
           return pro;
         }
-        pro = u3n_nock_on(u3k(bus), u3k(nex));
+        pro = _n_nock_on(u3k(bus), u3k(nex));
 
         u3z_save_2(c3__nock, bus, nex, pro);
         u3z(bus); u3z(nex);
@@ -93,7 +98,7 @@ _cn_hint(u3_noun zep,
     case c3__sole: {
       u3z(hod);
       {
-        u3_noun pro = u3n_nock_on(bus, nex);
+        u3_noun pro = _n_nock_on(bus, nex);
 
         // return u3z_uniq(pro);
         return pro;
@@ -102,12 +107,10 @@ _cn_hint(u3_noun zep,
   }
 }
 
-extern u3_noun BAD;
-
-/* u3n_nock_on(): produce .*(bus fol).  Do not virtualize.
+/* _n_nock_on(): produce .*(bus fol).  Do not virtualize.
 */
 u3_noun
-u3n_nock_on(u3_noun bus, u3_noun fol)
+_n_nock_on(u3_noun bus, u3_noun fol)
 {
   u3_noun hib, gal;
 
@@ -120,8 +123,8 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
     if ( c3y == u3r_du(hib) ) {
       u3_noun poz, riv;
 
-      poz = u3n_nock_on(u3k(bus), u3k(hib));
-      riv = u3n_nock_on(bus, u3k(gal));
+      poz = _n_nock_on(u3k(bus), u3k(hib));
+      riv = _n_nock_on(bus, u3k(gal));
 
       u3a_lose(fol);
       return u3i_cell(poz, riv);
@@ -151,8 +154,8 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
       c3_assert(!"not reached");
 
       case 2: {
-        u3_noun nex = u3n_nock_on(u3k(bus), u3k(u3t(gal)));
-        u3_noun seb = u3n_nock_on(bus, u3k(u3h(gal)));
+        u3_noun nex = _n_nock_on(u3k(bus), u3k(u3t(gal)));
+        u3_noun seb = _n_nock_on(bus, u3k(u3h(gal)));
 
         u3a_lose(fol);
         bus = seb;
@@ -164,7 +167,7 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
       case 3: {
         u3_noun gof, pro;
 
-        gof = u3n_nock_on(bus, u3k(gal));
+        gof = _n_nock_on(bus, u3k(gal));
         pro = u3r_du(gof);
 
         u3a_lose(gof); u3a_lose(fol);
@@ -175,7 +178,7 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
       case 4: {
         u3_noun gof, pro;
 
-        gof = u3n_nock_on(bus, u3k(gal));
+        gof = _n_nock_on(bus, u3k(gal));
         pro = u3i_vint(gof);
 
         u3a_lose(fol);
@@ -184,7 +187,7 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
       c3_assert(!"not reached");
 
       case 5: {
-        u3_noun wim = u3n_nock_on(bus, u3k(gal));
+        u3_noun wim = _n_nock_on(bus, u3k(gal));
         u3_noun pro = u3r_sing(u3h(wim), u3t(wim));
 
         u3a_lose(wim); u3a_lose(fol);
@@ -197,7 +200,7 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
 
         u3x_trel(gal, &b_gal, &c_gal, &d_gal);
         {
-          u3_noun tys = u3n_nock_on(u3k(bus), u3k(b_gal));
+          u3_noun tys = _n_nock_on(u3k(bus), u3k(b_gal));
           u3_noun nex;
 
           if ( 0 == tys ) {
@@ -218,7 +221,7 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
 
         u3x_cell(gal, &b_gal, &c_gal);
         {
-          u3_noun bod = u3n_nock_on(bus, u3k(b_gal));
+          u3_noun bod = _n_nock_on(bus, u3k(b_gal));
           u3_noun nex = u3k(c_gal);
 
           u3a_lose(fol);
@@ -234,7 +237,7 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
 
         u3x_cell(gal, &b_gal, &c_gal);
         {
-          u3_noun heb = u3n_nock_on(u3k(bus), u3k(b_gal));
+          u3_noun heb = _n_nock_on(u3k(bus), u3k(b_gal));
           u3_noun bod = u3nc(heb, bus);
           u3_noun nex = u3k(c_gal);
 
@@ -251,8 +254,12 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
 
         u3x_cell(gal, &b_gal, &c_gal);
         {
-          u3_noun seb = u3n_nock_on(bus, u3k(c_gal));
-          u3_noun pro = u3j_kick(seb, b_gal);
+          u3_noun seb = _n_nock_on(bus, u3k(c_gal));
+          u3_noun pro;
+         
+          u3t_off(noc_o);
+          pro = u3j_kick(seb, b_gal);
+          u3t_on(noc_o);
 
           if ( u3_none != pro ) {
             u3a_lose(fol);
@@ -288,7 +295,7 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
             u3_noun d_gal = q_gal;
 
             zep = u3k(b_gal);
-            hod = u3n_nock_on(u3k(bus), u3k(c_gal));
+            hod = _n_nock_on(u3k(bus), u3k(c_gal));
             nex = u3k(d_gal);
           }
           else {
@@ -301,13 +308,17 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
           }
 
           u3a_lose(fol);
-          return _cn_hint(zep, hod, bus, nex);
+          return _n_hint(zep, hod, bus, nex);
         }
       }
 
       case 11: {
-        u3_noun gof = u3n_nock_on(bus, u3k(gal));
-        u3_noun val = u3m_soft_esc(u3k(gof));
+        u3_noun gof = _n_nock_on(bus, u3k(gal));
+        u3_noun val;
+
+        u3t_off(noc_o);
+        val = u3m_soft_esc(u3k(gof));
+        u3t_on(noc_o);
 
         if ( !_(u3du(val)) ) {
           u3m_bail(u3nt(1, gof, 0));
@@ -328,6 +339,20 @@ u3n_nock_on(u3_noun bus, u3_noun fol)
   }
 }
 
+/* u3n_nock_on(): produce .*(bus fol).  Do not virtualize.
+*/
+u3_noun
+u3n_nock_on(u3_noun bus, u3_noun fol)
+{
+  u3_noun pro;
+
+  u3t_on(noc_o);
+  pro = _n_nock_on(bus, fol);
+  u3t_off(noc_o);
+
+  return pro;
+}
+
 /* u3n_kick_on(): fire `gat` without changing the sample.
 */
 u3_noun
diff --git a/n/r.c b/n/r.c
index 7fa79fecb..9bf9881a8 100644
--- a/n/r.c
+++ b/n/r.c
@@ -55,21 +55,25 @@ _frag_deep(c3_w a_w, u3_noun b)
 **   Return fragment (a) of (b), or u3_none if not applicable.
 */
 u3_weak
-u3r_at(u3_atom a,
-         u3_noun b)
+u3r_at(u3_atom a, u3_noun b)
 {
   c3_assert(u3_none != a);
   c3_assert(u3_none != b);
 
+  u3t_on(far_o);
+
   if ( 0 == a ) {
+    u3t_off(far_o);
     return u3_none;
   }
 
   if ( _(u3a_is_cat(a)) ) {
+    u3t_off(far_o);
     return _frag_word(a, b);
   }
   else {
     if ( !_(u3a_is_pug(a)) ) {
+      u3t_off(far_o);
       return u3_none;
     }
     else {
@@ -83,11 +87,15 @@ u3r_at(u3_atom a,
         b = _frag_deep(a_u->buf_w[len_w - 1], b);
 
         if ( u3_none == b ) {
+          u3t_off(far_o);
+
           return b;
         } else {
           len_w--;
         }
       }
+      u3t_off(far_o);
+
       return b;
     }
   }
diff --git a/n/t.c b/n/t.c
index de85fdf47..f111510d3 100644
--- a/n/t.c
+++ b/n/t.c
@@ -179,24 +179,37 @@ _t_samp_process(u3_road* rod_u)
 }
 #endif
 
-int SAM;
-int SAZ;
-
 /* u3t_samp(): sample.
 */
 void
 u3t_samp(void)
 {
+  u3C.wag_w &= ~u3o_debug_cpu;
+
   //  Profile sampling, because it allocates on the home road,
   //  only works on when we're not at home.
   //
-  c3_assert(!SAM);
-  SAM = 1;
-  SAZ = 0;
-
   if ( &(u3H->rod_u) != u3R ) {
+    c3_l      mot_l;
     u3a_road* rod_u;
-   
+  
+    if ( _(u3T.mal_o) ) {
+      mot_l = c3_s3('m','a','l');
+    }
+    else if ( _(u3T.far_o) ) {
+      mot_l = c3_s3('f','a','r');
+    }
+    else if ( _(u3T.noc_o) ) {
+      c3_assert(!_(u3T.glu_o));
+      mot_l = c3_s3('n','o','c');
+    }
+    else if ( _(u3T.glu_o) ) {
+      mot_l = c3_s3('g','l','u');
+    }
+    else {
+      mot_l = c3_s3('f','u','n');
+    }
+
     rod_u = u3R;
     u3R = &(u3H->rod_u);
     {
@@ -206,11 +219,11 @@ u3t_samp(void)
       if ( 0 == u3R->pro.day ) { 
         u3R->pro.day = u3v_do("doss", 0);
       }
-      u3R->pro.day = u3dc("pi-noon", lab, u3R->pro.day);
+      u3R->pro.day = u3dt("pi-noon", mot_l, lab, u3R->pro.day);
     }
     u3R = rod_u;
   }
-  SAM = 0;
+  u3C.wag_w |= u3o_debug_cpu;
 }
 
 /* u3t_come(): push on profile stack; return yes if active push.  RETAIN.
@@ -263,16 +276,26 @@ void _ct_sigaction(c3_i x_i)
   u3t_samp();
 }
 
+/* u3t_init(): initialize tracing layer.
+*/
+void
+u3t_init(void)
+{
+  u3T.noc_o = c3n;
+  u3T.glu_o = c3n;
+  u3T.mal_o = c3n;
+  u3T.far_o = c3n;
+}
+
 /* u3t_boot(): turn sampling on.
 */
 void
 u3t_boot(void)
 {
-  if ( u3C.wag_w & u3o_debug_cpu ) {
+  if ( u3C.wag_w & u3o_debug_cpu ) { 
 #if defined(U3_OS_osx)
 #if 1
     {
-      SAZ = 0;
       struct itimerval itm_v;
       struct sigaction sig_s;
       sigset_t set;